1. Field of Invention
This invention relates to improvements in methods and apparatuses for dynamic information storage or retrieval, and more particularly to improvements in methods and circuitry for biasing a data transducer, or head, amplifier used in mass data storage devices, hard disk drive devices, or the like, and still more particularly to improvements in driver circuitry and methods for biasing an amplifier for a tunneling giant magneto-resistive (TGMR) type of such data transducer.
2. Relevant Background
Mass data storage devices include tape drives, as well as hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Many applications are still being developed. Applications for hard disk drives are increasing in number, and are expected to further increase in the future.
Typically, in the construction of a hard disk drive, a data transducer, or head is located in proximity to a spinning platter, or disk, on which a magnetic material has been emplaced. The magnetic material contains a pattern of rings along which the domains of the magnetic material are selectively oriented in accordance with the recorded data, so that as the head flies over the magnetic material and along the rings, it can detect the orientation of the domains to enable the data to be read and decoded.
Recently, magneto-resistive (MR) heads have been finding increasing use in such disk drive applications. The term xe2x80x9cmagneto-resistivexe2x80x9d refers to the change in resistivity of metals in the presence of a magnetic field. MR heads are gaining popularity primarily because MR heads efficiently convert magnetization changes into sufficiently high current or voltage with a minimum amount of noise, detect signals at high densities with a negligible loss in signals, and are cost-effective.
Moreover, MR-sensor technology is extendable to very high disk drive densities. Among the many advantages of the MR heads is the fact that they are essentially independent of the velocity of the disk medium, because they measure the flux from the medium, in contrast, for example, to inductive heads, which measure the change in flux with time. They can therefore find wide use in such applications as lap top computers, which have a relatively slowly rotating hard disk, as will as in high-end personal computers, which have rapidly rotating disks.
Very recently, tunneling, giant, magneto-resistive (TMGR) heads have been introduced, which are also gaining widespread popularity. TGMR heads are capable of detecting extremely feeble magnetic signals, using a ferromagnetic tunneling effect to produce a current flow that significantly reduces the resistance of the head. However, unlike normal MR heads, which have resistances in the range of about 30 to 60 ohms, TGMR heads have resistances about 10 times as large, for example, in the range of about 300 to 600 ohms. Consequently, MR typical head biasing circuits experience difficulties in biasing such TGMR heads.
For example, the head amplifier may be overbiased using the same circuit that was used for an ordinary MR head. Also, due to the increased resistance of the head, the time constants to charge the various parts of the biasing circuitry have larger time constants, and therefore, take longer to respond to changes, particularly on power up or turn-on of the circuit.
What is needed, therefore, is a biasing circuit that can be used in conjunction with a TGMR head amplifier that has reduced time constants, and which is not susceptible to overbiasing the head amplifier.
In light of the above, therefore, it is an advantage of the invention that the impedance of the MR head circuit can be controlled to be a relatively constant value regardless of whether the MR head amplifier is turned on or off.
It is another advantage of the invention that the current that flows in an MR head remains relatively constant when the head is turned on or off in operation.
It is another advantage of the invention that current spikes that normally occur when an MR head amplifier is turned on or off are reduced or eliminated.
It is yet another advantage of the invention that since current spikes and high currents that otherwise may flow in the head are reduced or eliminated, risk of damage to the MR head from such currents is also reduced or eliminated.
These and other objects, features, and advantages will become apparent to those skilled in the art from the following detailed description, when read in conjunction with the accompanying drawings and appended claims.
According to a broad aspect of the invention, an impedance controlling circuit is provided for connection across an MR head. The MR head may be, for example, a TGMR head, and may have a resistance of, for instance, about 600 ohms. The circuit includes two current paths, each including a control transistor, a current path resistor, and a biasing circuit in series. Each side of the MR head is connected between a respective one of the current path resistors and the biasing circuits. A shunt resistor is connected between respective nodes between the control transistors and the current path resistors in each of the current paths, so that when the control transistors are conducting, the current path resistors and the shunt resistor shunt the MR head.
According to another broad aspect of the invention, an impedance controlling circuit is provided for connection across a TGMR head. The circuit includes A TGMR head and a current stealing circuit connected to the TGMR head that operates to conduct an amount of current through the TGMR head when the TGMR head amplifier is turned off that is substantially equal to a current in the TGMR head when the TGMR head amplifier is turned on. The impedance controlling circuit may include a resistor connected between a pair of TGMR head biasing current paths that operate when the TGMR head amplifier is turned on, whereby the resistor provides a current flow path through the pair of TGMR head biasing current paths when the TGMR head amplifier is turned off.
According to yet another broad aspect of the invention, a method is presented for operating a mass data storage device. The method includes providing a magnetic media on which data may be selectively written, providing a TGMR head in proximity to the magnetic media for at least reading data from the magnetic media, and providing a current stealing circuit in connection with the TGMR head amplifier that operates to conduct an amount of current through the TGMR head when the TGMR head amplifier is turned off that is substantially equal to a current in the TGMR head when the TGMR head amplifier is turned on. The providing a current stealing circuit may include providing a resistor between a pair of TGMR head biasing current paths that operate when the TGMR head amplifier is turned on, whereby the resistor provides a current flow path through the pair of TGMR head biasing current paths when the TGMR head amplifier is turned off.
According to yet another broad aspect of the invention, a mass data storage device is presented. The mass data storage device has a magnetic media on which data may be selectively written and a TGMR head in proximity to the magnetic media for at least reading data from the magnetic media. A current stealing circuit is in connection with the TGMR head that operates to conduct an amount of current through the TGMR head when the TGMR head amplifier is turned off that is substantially equal to a current in the TGMR head when the TGMR head amplifier is turned on. The current stealing circuit may include a resistor between a pair of TGMR head biasing current paths that operate when the TGMR head amplifier is turned on, whereby the resistor provides a current flow path through the pair of TGMR head biasing current paths when the TGMR head amplifier is turned off.